Referring to FIG. 1, which shows the offset phenomenon of an operational amplifier. A signal Vo symmetrical to zero voltage is inputted to the operational amplifier 1, an ideal output should be a signal AmpVosymmetrical to zero voltage (as shown on the top right of FIG. 1), “Amp” represents the amplification factor of the operational amplifier 1. However, the real output will often be AmpVo+Voffset(as shown on the bottom right of FIG. 1) which is deviated from the zero votage due to some design or manufacturing defects of the operational amplifier 1. Voffsetis the offset generated by the operational amplifier 1.
Due to the manufacturing deviation of the operational amplifier 1, sometimes the value of the Voffset is positive, but sometimes it is negative, so it will have an unpredictable influence over the circuit connected to the operational amplifier 1.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.